If you look at the data from that period, government expenditures as a share of GDP went down in the 1990s -- due to the "peace dividend" on the numerator, and the GDP growth of the dot-com boom on the denominator. We had 4 successive years (1996, 1997, 1998, and 1999) with GDP growth topping 4%.
This high GDP growth also naturally led to a boost in tax revenues (more on that below).
Here's total federal spending in the 1990s, as % GDP:
And here's Defense spending by itself during that period:
Defense spending in 1990 was 5.69% of GDP. Defense spending in 2000 was 3.48% of GDP. So it went down by 2.2% of GDP -- which is a massive number.
By comparison, total federal spending in 1990 was 20.83% of GDP, total federal spending in 2000 was 17.34%. So it went down by 3.49%. And defense spending reductions accounted for 63% of that.
On the revenue side, revenues were flat between 1990-1996. They were 17.16% in 1990 and 17.87% in 1996.
But that's about the time the dot-com boom started happening and tax revenues got a jolt. In 1997 they were 18.23%, and in 2000 they were 19.63%.
Tax year 2000 is the only year since 1950 where federal tax revenues eclipsed 19% of GDP. And there have only be 10 years (out of 74) where they eclipsed 18%.